1. Field of the Invention
This invention relates in general to a corrugated horn radiator which has a transition zone mounted between a smooth-walled feed wave guide having a constant cross-section and a funnel radiator having regular periodic corrugation structures which have depths of corrugations less than a quarter-wave length with respect to the lowest operating frequency to be transmitted.
2. Description of the Prior Art
For the operation of transmission/reception antennas having emission and two orthogonal polarizations, it is necessary to employ radiators preferably having low cross-polarization. A rotational-symmetrical radiation field and a low reflection factor are presumed. Corrugated horn radiators are used in a wide range of applications in microwave antennas because of these favorable electrical properties. Corrugated horn radiators previously have maximum band width of approximately 20% and do not have broad band characteristics and have not had good cross-polarization characteristics. Several prior art corrugated horn radiators function with a depth of corrugation that is greater than one-quarter wave length. Also, corrugated horn radiators are known in which the corrugations for the lower frequency band are less than a quarter wave length in depth as described in the publication IEEE Transactions, Vol. AP-26, No. 2, March 1978, pages 367 through 372. Such described corrugated horn radiators have a relatively good radiation diagram symmetry in the lower frequency range and a low reflection factor in the upper frequency range. However, they do not provide sufficient matching in the lower frequency range and have diagram asymmetry and a higher cross-polarization in the upper frequency range.